Brother HL 5370DW - Manual (Page 115)

Routine Maintenance
105
6
f Put the drum unit and toner cartridge assembly back in the printer.
g
Press and hold down the Go for about 4 seconds until all the LEDs light up. Once all four LEDs are lit,
release Go.
IMPORTANT
Do not reset the drum counter when you only replace the toner cartridge.
h Close the front cover.
i Make sure that the Drum LED is now off.